Fibre Optic Vibration and Acceleration Sensor

Abstract

The invention relates to fibre optic vibration and acceleration sensors comprising a dielectric mirror and a first light-guiding fibre connected to a coupler, the coupler being further connected via second light-guiding fibres to a light source and a detector that generates a voltage from incident light.

Said sensors are characterised in particular by their simple implementation.

For this purpose, a free end region of the first fibre is spaced apart from the dielectric mirror such that an edge of the dielectric mirror is located in the emergent light of the first fibre. In the unexcited state, the voltage of the detector generated from the light incident on the end of the first fibre is smaller than the voltage generated by the detector when the aperture cone of the first fibre is completely covered by the dielectric mirror and there is thus maximum reflection. Said voltage is a measure of the fibre optic vibration and acceleration sensor.

A fibre is itself therefore used as a vibration-sensitive element.

Claims

1. Fibre optic vibration and acceleration sensor comprising a dielectric mirror (7) and at least a first light-guiding fibre connected to a coupler (3), the coupler (3) being further connected via second light-guiding fibres to a light source (5) and a detector (8) that generates a voltage from incident light, characterised in that a free end region of the first fibre is spaced apart from the dielectric mirror (7) such that an edge of the dielectric mirror (7) is located in the emergent light of the first fibre such that, in the unexcited state, the voltage of the detector (8) generated from the light incident on the end of the first fibre is smaller than the voltage generated by the detector (8) when the aperture cone of the first fibre is completely covered by the dielectric mirror (7) and there is thus maximum reflection, and said voltage is a measure of the fibre optic vibration and acceleration sensor.

2. Fibre optic vibration and acceleration sensor according to claim 1, characterised in that a first fastening means (2) for the first fibre and a second fastening means (11) for the dielectric mirror (7) are interconnected.

3. Fibre optic vibration and acceleration sensor according to claim 2, characterised in that the first fastening means (2) is a sleeve (13) in a tubular part (12), and in that the dielectric mirror (7) is located on the cross-sectional surface of the tubular part (12) that is opposite the sleeve (13), and therefore the tubular part (12) is a fastening means of the sleeve (13) and is the second fastening means (11).

4. Fibre optic vibration and acceleration sensor according to claim 1, characterised in that the fibre and the dielectric mirror (7) are connected to the fastening means (2, 11) by gluing and/or clamping.

5. Fibre optic vibration and acceleration sensor according to claim 1, characterised in that the voltage generated by the detector (8) when the aperture cone of the first fibre is completely covered by the dielectric mirror (7) and there is thus maximum reflection is a first voltage, and the voltage of the detector (8) generated from the light incident on the end of the first fibre in the unexcited state is a second voltage.

6. Fibre optic vibration and acceleration sensor according to claim 5, characterised in that the second voltage is 50% of the first voltage.

7. Fibre optic vibration and acceleration sensor according to claim 1, characterised in that the dielectric mirror (7) has at least one sharp, straight and smooth edge, which is located in the emergent light of the first fibre.

8. Fibre optic vibration and acceleration sensor according to claim 1, characterised in that in the first ends of the second light-guiding fibres are located beside one another in the coupler (3), in that the end of the first fibre opposite the free end (6) is arranged at the first ends of the second fibres such that the end of the first fibre overlaps the ends of the second fibres, and in that the second end of one second fibre is coupled to the light source (5) and the second end of the other second fibre is coupled to the detector (8).

9. Fibre optic vibration and acceleration sensor according to claim 1, characterised in that the free end region of the first fibre is a vibratory structure, and in that the resonant frequency of the structure is determined by the length, diameter and modulus of elasticity of the free end region of the first fibre such that an external vibration acting on the fibre optic vibration and acceleration sensor excites the free end region of the first fibre so as to vibrate at the same frequency, the amplitude of the vibration being relatively constant and proportional to the intensity of the excitation in a frequency range smaller than the resonant frequency of the structure, and sharply increasing close to the resonant frequency.

10. Fibre optic vibration and acceleration sensor according to claim 1, characterised in that the second fastening means (11) has at least one guide element for the dielectric mirror (7), such that the dielectric mirror (7) can be movably guided relative to the end of the first fibre and fastened after positioning.

11. Fibre optic vibration and acceleration sensor according to claim 1, characterised in that the free end regions of first fibres are spaced apart from the dielectric mirror (7), the distances of the ends of the first fibres from the edge of the dielectric mirror (7) being different, and in that the first fibres are connected via at least one coupler (3) and light-guiding fibres to at least one detector (8) and at least the light source (5) or one light source (5) in each case.

12. Fibre optic vibration and acceleration sensor according to claim 1, characterised in that the free end regions of first fibres are arranged in parallel with one another and so as to be spaced apart from the dielectric mirror (7), the ends of the first fibres pointing towards an edge of the dielectric mirror (7), and in that the first fibres are connected via at least one coupler (3) and light-guiding fibres to at least one detector (8) and at least the light source (5) or one light source (5) in each case.

13. Fibre optic vibration and acceleration sensor according to claim 1, characterised in that the free end regions of first fibres are spaced apart from the dielectric mirror (7), and in that the ends of the first fibres point towards two edges of the dielectric mirror (7) that are arranged at an angle to one another, and in that the first fibres are connected via at least one coupler (3) and light-guiding fibres to at least one detector (8) and at least the light source (5) or one light source (5) in each case.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In the drawings:

[0040] FIG. 1 shows a fibre optic vibration and acceleration sensor,

[0041] FIG. 2 is a diagram showing amplitude as a function of frequency,

[0042] FIG. 3 shows an arrangement of a first glass fibre and a dielectric mirror,

[0043] FIG. 4 shows mutually parallel end regions of two first glass fibres with a dielectric mirror, a coupler, a light source, a detector and a control unit,

[0044] FIG. 5 shows a dielectric mirror with two parallel light spots produced by two first glass fibres,

[0045] FIG. 6 shows a dielectric mirror with two light spots arranged over the corner, produced by two first glass fibres, and

[0046] FIG. 7 shows mutually parallel end regions of two first glass fibres with a dielectric mirror, couplers, light sources, detectors and a control unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] A fibre optic vibration and acceleration sensor substantially consists of a dielectric mirror 7, a first glass fibre 1 as a first fibre, a coupler 3, a light source 5, a detector 8, and second fibres as a second glass fibre 4 and a third glass fibre 9.

[0048] FIG. 1 schematically shows a fibre optic vibration and acceleration sensor.

[0049] The first glass fibre 1 it itself used as a vibration-sensitive element, and is secured at one end and directed towards the dielectric mirror 7 for this purpose. The distance between the first glass fibre 1 and the dielectric mirror 7, and the edge thereof, determines the sensitivity and the directional orientation of the fibre optic vibration and acceleration sensor.

[0050] The first glass fibre 1 is secured at one end by clamping or gluing in a first fastening means 2 and is connected to a light source 5 by means of the second glass fibre 4 via the coupler 3. For this purpose, the first fastening means 2 may be a body 2 having a bore or recess for receiving a region of the first glass fibre 1. Light from the light source 5, which is preferably a light-emitting diode, is coupled into the first glass fibre 4 via the second glass fibre 4 and the coupler 3 and emerges at the end 6 at an opening angle of approximately 20 degrees. This opening angle corresponds to the numerical aperture of the first glass fibre 1 and can be selected depending on the fibre type. The light reflected by the dielectric mirror 7 is coupled into the first glass fibre 1 and reaches the detector 8 via the coupler 3 and the third glass fibre 9, which detector generates an equivalent electrical voltage therefrom. For this purpose, the first ends of the second glass fibre 4 and the third glass fibre 9 are arranged beside one another in the coupler 3. The end of the first glass fibre 1 opposite the free end is located at the first ends of the second glass fibre 4 and the third glass fibre 9 such that the end of the first glass fibre 1 overlaps the ends of the second glass fibre 4 and the third glass fibre 9.

[0051] The light source 5 and the detector 8 are connected to a control unit 10. The latter may be a microcomputer.

[0052] FIG. 2 schematically shows a diagram showing amplitude as a function of frequency.

[0053] The glass fibre 1 secured at one end is a vibratory structure of which the resonant frequency is determined by the length, diameter and modulus of elasticity. An external force/acceleration at the frequency f excites the first glass fibre 1 so as to vibrate at this frequency f. The amplitude A of the vibration is relatively constant and proportional to the intensity of the excitation between the frequencies f1 and f2, and drastically increases close to the resonant frequency f3.

[0054] FIG. 3 schematically shows an arrangement of a first glass fibre 1 and a dielectric mirror 7.

[0055] The dielectric mirror 7 is spaced apart from the end 6 of the first glass fibre 1. The mirror has a sharp and smooth edge. The dielectric mirror 7 is mechanically connected to the clamping/gluing of the first glass fibre 1. There may, as shown by way of example in FIG. 3, be a tubular part 12 as a second fastening means 11. The first attachment means 2 for the first glass fibre 1 and the second attachment means 11 for the dielectric mirror 7 are interconnected as a sleeve 13 in the tubular part 12 and as the tubular part 12 itself. The sleeve 13 is located in the tubular part 12. Furthermore, the dielectric mirror 7 is arranged on the cross-sectional surface opposite the sleeve 13, and thus on an edge 14 of the tubular part 12.

[0056] The mirror is now adjusted and fixed as follows:

[0057] When the mirror 7 completely covers the aperture cone of the first glass fibre 1, a maximum proportion of the light is reflected back into the first glass fibre 1 and reaches the detector 8 via the coupler 3 and the third glass fibre 9 and generates an electrical voltage at the detector 8. The sharp-edged dielectric mirror 7 is now adjusted and fixed such that the output voltage of the detector 8 is 50% of the voltage when the aperture cone is completely covered. The sharp edge of the dielectric mirror 7 is oriented perpendicularly to the gravitational field of the earth. During the adjustment, the sharp edge points towards the gravitational field of the earth.

[0058] If the tubular part 12 is now rotated in parallel with the axis of the first glass fibre 1 by +90 or90, the first glass fibre 1 bends on account of its own weight and changes the coupling relationships between the sharp-edged dielectric mirror 7 and the first glass fibre 1. The resulting voltage difference corresponds to the simple gravity of 9.81 m/s.sup.2 and thus allows easy calibration.

[0059] If the first glass fibre 1 is now excited by mechanical vibrations, it also vibrates at the frequency and in the direction of the excitation. Movements of the first glass fibre 1 and the end 6 thereof that are parallel to the sharp edge of the dielectric mirror 7 do not result in any change in the light intensity on the detector 8, while movements perpendicular to the sharp edge of the dielectric mirror 7 result in voltage changes that are proportional to the gravitational acceleration.

[0060] The sensor is therefore directionally selective and insensitive to electromagnetic fields.

[0061] Instead of the tubular part 12 as a fastening means, a U-shaped structural element can also be used as a fastening means. The limbs are in this case the first fastening means 2 for the first glass fibre 1 and the second fastening means 11 for the dielectric mirror 7.

[0062] The second fastening means 11 can have at least one guide element for the dielectric mirror 7, such that said mirror can be movably guided relative to the end of the first glass fibre 1 and fastened after positioning. Of course, there may also be two guide elements which are mutually spaced such that the dielectric mirror 7 can be movably guided therebetween. After the positioning, the dielectric mirror 7 can be easily adhesively secured in the guide element(s).

[0063] FIG. 4 schematically shows mutually parallel end regions of two first glass fibres 1a, 1b with a dielectric mirror 7, a coupler 3, a light source 5, a detector 8 and a control unit 10.

[0064] In a first embodiment, in a fibre optic vibration and acceleration sensor, the free end regions of two first glass fibres 1a, 1b are spaced apart from the dielectric mirror 7. The distances of the ends of the first glass fibres 1a, 1b from the edge of the dielectric mirror 7 are the same or different.

[0065] FIG. 5 schematically shows a dielectric mirror 7 with two parallel light spots 15a, 15b produced by two first glass fibres 1a, 1b.

[0066] The free end regions of the first glass fibres 1a, 1b can be arranged in parallel with one another and so as to be spaced apart from the dielectric mirror 7 such that the ends of the first glass fibres 1a, 1b point towards an edge of the dielectric mirror 7.

[0067] FIG. 6 schematically shows a dielectric mirror 7 with two light spots 15a, 15b produced by two first glass fibres 1a, 1b.

[0068] In a first embodiment, in a fibre optic vibration and acceleration sensor, the free end regions of first glass fibres 1a, 1b are spaced apart from the dielectric mirror 7. The ends of the first glass fibres 1a, 1b point towards two edges of the dielectric mirror 7 that are arranged at an angle to one another. FIG. 3 shows the light spots 15a, 15b from the first glass fibres 1a, 1b. The distances of the ends of the first glass fibres 1a, 1b from the dielectric mirror may be the same or different. A vibration or acceleration acting in two axes can thus be measured.

[0069] In a first variant, the first glass fibres 1a, 1b of the first and the second embodiment can be connected in each case via a coupler 3 and light-guiding fibres as second glass fibres 4, 9 to at least one detector 8 and at least the light source 5 or one light source 5 in each case.

[0070] FIG. 7 schematically shows mutually parallel end regions of two first glass fibres 1a, 1b with a dielectric mirror 7, couplers 3, light sources 5, detectors 8 and a control unit 10.

[0071] In a second variant, the first glass fibres 1a, 1b of the first and the second embodiment can be connected in each case via a coupler 3 or mixer and light-guiding fibres as second glass fibres 4, 9 to at least one detector 8 and a light source 5. The detectors 8 and the light sources 5 of the first glass fibres 1a, 1b are connected to the control unit 10. The light sources 5 can also be operated in a clocked manner such that it is possible to assign a reflection at the dielectric mirror 7 that can be assigned to the corresponding first glass fibre 1. This can also be done by means of light sources 5 of different wavelengths.

[0072] In further variants, a plurality of first glass fibres 1 can each be connected via a coupler 3 or mixer and light-guiding fibres as second glass fibres 4, 9 to at least one detector 8 and a light source 5. The detectors 8 and the light sources 5 of the first glass fibres 1 are connected to the control unit 10. Dielectric mirrors 7 arranged at an angle to one another are arranged for this purpose. For instance, the dielectric mirrors 7 can form an L, T, U or O shape in cross section. This allows measurements to also be made in three axes. The light sources 5 can also be operated in a clocked manner in this case such that it is possible to assign a reflection at the dielectric mirrors 7 that can be assigned to the corresponding first glass fibre 1. This can also be done by means of light sources 5 of different wavelengths.

LIST OF REFERENCE NUMERALS

[0073] 1 first glass fibre
2 first fastening means
3 coupler
4 second glass fibre
5 light source
6 end of the first glass fibre
7 mirror
8 detector
9 third glass fibre
10 control unit
11 second fastening means
12 tubular part
13 sleeve
14 edge
15 light spot